There are many systems used to conduct gas-solid processes such as gas-particle energy recovery and regeneration, gas-solid chemical reactions, gasification, adsorption, drying, gas absorption and distillation.
Examples of these systems are rotary dryers and rotary kilns, but these are not efficient gas-solid contactors. Other systems such as fluidised beds and circulating fluidised beds have been used instead. However, these systems have their own deficiencies such as an increased pressure drop and contacting inefficiency.